Subsequently Horizon Lines, Inc (NYSE:HRZ) issued a statement that said it "confirmed federal agents today served search warrants and a grand jury subpoena relating to an investigation of pricing practices of ocean carriers operating in the Puerto Rico trade."

Horizon said it is "cooperating fully with the government officials. The company has not been informed of the specific subject matter of the inquiry, being conducted by the U.S. Department of Justice's Antitrust Division."

Horizon Lines says it does not expect the government inquiry to impact the service levels provided to its customers.

Crowley Maritime Corp. is another subject of the federal investigation into pricing practices of ocean carriers operating in the Puerto Rico trade.

The Jacksonville Journal reports that in a prepared statement, Crowley officials said federal investigators are conducting an antitrust investigation and that Crowley will cooperate.

"Certain records were obtained by investigators Thursday," the company said in the statement. "Crowley intends to cooperate with investigators and is confident that it has acted appropriately in all respects. Neither Crowley, nor its employees, have been identified as targets of this investigation."

"Matson Navigation, A&B's ocean transportation subsidiary, does not operate vessels in the Puerto Rico trade. However, Matson has been informed by the Department of Justice that it will receive a subpoena for documents related to domestic ocean carriage. We will cooperate fully with the Department of Justice."